Computer Architecture
Computer Architecture
Computer Architecture
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Mutual Exclusion<br />
Proposals for achieving mutual exclusion (continued)<br />
• Test and Set Lock (TSL)<br />
Atomic operation at machine level. Cannot be interrupted. TSL reads the content of the<br />
memory word lock into register R and then stores a nonzero value at the memory<br />
address lock. The memory bus is locked, no other process(or) can access lock.<br />
enter_region: TSL R, lock<br />
CMP R, #0<br />
JNZ enter_region<br />
RET<br />
leave_region: MOV lock, #0<br />
RET<br />
indivisible operation<br />
Pseudo assembler listing providing the functions enter_region() and leave_region().<br />
<strong>Computer</strong> <strong>Architecture</strong> WS 06/07 Dr.-Ing. Stefan Freinatis<br />
IPC<br />
CPU must support TSL<br />
Busy waiting
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